Method and apparatus for separating particles from a liquid

ABSTRACT

A method and device for separating particles from a liquid having particles therein, using a filter sized to permit the liquid to flow through pores, while retaining a substantial portion of the particles on the filter, with an absorbent layer contacting the back of the filter to facilitate liquid movement away from the particles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/720,389, filed Mar. 9, 2010, issuing on Jan. 10, 2012 as U.S. Pat.No. 8,092,691, and claims the benefit of U.S. Provisional ApplicationSer. No. 61/158,625, filed on Mar. 9, 2009, the disclosures of both arehereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention generally relates to devices and methods for separatingparticles from a liquid containing particles therein, and moreparticularly for separating algae from water.

BACKGROUND OF THE INVENTION

There are thousands of strains of algae, both naturally occurring andgenetically modified, known to exist. A significant portion of thesestrains are known to produce various organic materials which can in turnhave commercial utility, such as but not limited to biodiesel,pharmaceutical and nutriceutical applications. The materials produced byalgae are sometimes formed within the cellular walls of the algae, butalternatively they may be excreted and available on the outside surfaceof the algae. In either case, to isolate the materials, it is usuallynecessary to first separate the algae from the medium in which theygrow, which is typically water based. The concentrated algae, also knownas an algae paste or cake, may be able to be processed containingamounts of residual water. Or, it may be preferred, or even necessary,to completely dry the algae prior to further processing.

A number of processes have been developed in conjunction with removingor separating algae at various levels of maturity from the growthmedium, again typically water based. The processes have includedflocculation, sedimentation, flotation, centrifugation, vibratoryseparation, micro-screening, filter press methods, belt press methods,and methods involving use of a dry bed. Occasionally, more than onemethod is used in combination. Generally, the above processes canrequire substantial energy input to effect separation, and the resultantproduct will still require further drying before processing to isolatethe desired organic material can begin.

In addition, practicing several of the above processes can createindirect disadvantages in the overall process of extracting organicmaterial from algae. For example, flocculation, sedimentation, andflotation methods generally require a batch strategy for harvestingalgae which requires removing most of the algae from the growth pond orvessel. This step results in substantially less algae in the pond orvessel to carry on the propagation process which negatively affectsproductivity. Alternatives to the batch strategy exist, such as the useof multiple tanks to create a semi-batch process. But, this alternativealso requires more space, capital and time. Also, several of the aboveprocesses can damage or destroy individual algae cells resulting fromthe stresses imposed by the separation process.

SUMMARY OF THE INVENTION

The invention can be generally described as a device for facilitatingseparation of particulate matter from a liquid containing theparticulate matter, such as water. In particular, algae can be separatedfrom carrier fluid, such as water; but other particulate materials canalso be separated from a liquid by use of the device. The invention alsocontemplates a method for effecting such a separation, again inreference not only to algae, but other particulate materials as well.The method effects separation at a relatively low expenditure of energy,and utilizes low differential pressure which minimizes damage to theparticles being separated.

The device comprises a filter which is positioned within a frame, withan absorbent layer located in contact with the filter to facilitateremoval of liquid such as water. The filter has upper and lowersurfaces, and pores which communicate between those surfaces. The poresof the filter are sized so that at least a substantial portion of theparticulate matter to be separated cannot penetrate substantially intothe pores. In the context of an application involving separating algaefrom the nutrient water, a mixture of algae in water is applied to theupper surface of the filter. Water begins to separate from the algae,flowing through pores in the filter to the lower surface of the filter.The absorbent layer is placed into contact with the lower surface of thefilter, and water contacting the absorbent layer is drawn away from thelower surface of the filter, thereby drawing more water through thepores from above. A dampened absorbent layer more efficiently removeswater from the lower surface of the filter than one which is dry.Because sufficient build-up of algae on the upper surface of the filtercan limit water flow, the filter optionally is moved relative to theinput point of algae and water. In addition, methods for facilitatingflotation of the particle to the surface of the liquid-particle mixturewill tend to concentrate the particles away from the upper surface ofthe filter and allow liquid to flow through the pores more easily. Also,because the capacity of the absorbent layer to absorb water is finite,optionally the absorbent layer is moved relative to the location on thefilter where water is flowing through the pores. The filter can moverelative to the input point for the algae and water, and the absorbentlayer can move relative to the filter either in the same direction butat a different rate, or in a different direction relative to the filter.Thus, the filter can move alone, the absorbent layer can move alone, orboth can move. As another alternative, the input point for the mixtureonto the filter can move relative to the filter, or multiple inputpoints can be used. Compared to conventional centrifuge methods ofseparating solid and liquid components of a mixture, the method ofseparating using this device on algae is expected to effect theseparation with a substantial energy reduction compared to centrifugalseparation, up to a 95% reduction, and to attain a higher solids contentin the concentrated product compared to centrifugal separation.

Further, this method uses a relatively low degree of differentialpressure to assist in facilitating water movement through the pores. Asa result, the particle is neither pushed nor pulled into the pores ofthe filter, and blinding or blocking of the pore inlets is negligible.In addition, the method imposes low deforming forces on the particle. Inthe case of separating algae from water, this feature assists inpreserving the structural integrity of the algae cells. This aspect ofthe method contributes to maintaining the contents, typicallyoil-bearing, of the algae for later processing. And, gentle drying ofthe algae can then place the algae in a dormant phase which allows forlater reanimation under growing conditions.

After a substantial portion of the water is separated from the particle,the particles remaining on the upper surface of the filter can befurther reduced in water content by one of a number of techniques, andthen removed from the filter for further processing. In the case ofalgae, one example of further processing is the extraction of organicmaterial from the algae. The filter can be configured on the device as acontinuous loop mounted on the frame, and the absorbent loop can also beconfigured as a continuous loop, or as a plurality of smaller continuousloops so that at least a portion of the absorbent layer makes contactwith a portion of the lower surface of the filter in operation. Waterabsorbed by the absorbent layer can be removed, and the layer reused, bypassing the layer between two rolls or similar components which extractthe entrained water from the layer. Intermittently, the filter,absorbent layer, or both, may be cleaned to remove any accumulation ofparticles over time by chemical or physical operations, and thereby openpartially or completely clogged pores. Because of the low differentialpressures employed in practicing the method, the filter can remain inoperation, even continuously, for long periods of time before cleaningor refurbishing is required.

As further described herein, the device and method of separating areprimarily discussed in connection with separating algae particles fromwater or similar growth medium, though the separation of other particlesand particle types is envisioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a frame configured with a screen andabsorbent layer, operating to receive a mixture of algae and water andseparate the components.

FIG. 2 is a perspective cross-section of the embodiment of FIG. 1, withthe algae and water omitted.

FIG. 3 is an elevational cross-section of the embodiment of FIG. 1.

FIG. 4 is a schematic cross-section as indicated in FIG. 3.

FIG. 5 is an enlarged schematic cross-section as indicated in FIG. 3.

FIG. 6 is a schematic representation of an embodiment of filtermaterial.

FIG. 7 is a detail schematic cross-section view of a portion of theembodiment of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to separating particles from a liquidcontaining particles therein, encompassing a device and a method ofprocessing. The invention utilizes a filter having an upper surface onwhich liquid containing particles, such as algae in water (an algalmixture), is placed. The filter further includes a lower surface andpores, with at least a portion of the pores extending from the uppersurface through to the lower surface. Further, the separation takesplace with low expenditure of energy. And, the separation operates at alow differential pressure, which imposes relatively slight stresses toindividual particles, minimizing damage to the particles. In the case ofseparating algae from water, the pores in the filter are sized to allowthe liquid to pass through the pores, while keeping algae on the topsurface. Some percentage of particles may pass through the pores, and apass-through amount of up to about 10% to about 15% of the particles isconsidered acceptable. The particles may partially or completely blocksome portion of the inlets of the pores, and thus the flow rate ofliquid through the pores may decrease with time. However, the lowdifferential pressures employed in practicing the method will generallynot cause severe or irreversible blockage of pores. And, agglomerationattributed to the reduction in moisture of the particle cake tends tolift those particles which may have caused some port blockage away fromthe pore inlets.

Depending on the flow rate of the mixture of particles and water ontothe filter prior to separation, the rate of the flow of liquid throughthe filter may result in formation of a pool of the algal mixture on topof the filter. This pool may form in a depression along the filtersurface by the exertion of a downward force from the mixture near thefilter's center width, in combination with slack in the filter createdby rotation of the rollers conveying the filter toward that portioncomprising the pool boundary. The pool is replenished with algal mixturefrom a source. The mixture can be either continually or intermittentlyreplenished, and can be introduced via a single input point or amultiplicity of points. Thus, for example, the mixture can flow onto thefilter and into the pool via a single inlet pipe, or via a manifoldwhich in turn supplies multiple inlet nozzles. Where the filter movesrelative to the input source, before the pores of the filter can becomeclogged from the volume of algae covering the filter, the availablefilter surface is replenished with fresh filter surface, while thefilter with the algae on its top surface is moved out of the pool ofretained particles and water, or away from the location where the algalmixture is introduced.

The area or portion of filter that now has algae on it, in the form of awet paste on its top surface through which water may still be flowing,is brought into contact with an absorbent layer on the lower surface ofthe filter. The absorbent layer may be moved relative to the location onthe filter through which water drains, to expose relatively dryabsorbent material to facilitate the absorption of the water flowingaround the algae and through the filter pores. Water absorption isfacilitated if the absorbent layer is damp, such that some residualwater is retained in the layer. After the absorbent layer makes contactwith the underside of the filter and removes water from around the algaeparticles, the algae cake contains far less water than it did before thebottom surface of the filter was brought into contact with the absorbentmaterial. The algae cake's water content can be further lowered ifdesired by other means, such as by adding heat or introducing an airflow such as with a heating element, a fan, a blower, a light source anacoustic device or a vacuum, which can be introduced either above orbelow the algae cake.

The algae may be collected from the filter in a variety of ways, forexample by bending the filter after sufficient drying so that the cakelifts off the filter surface. Other treatments which facilitatecollection of the algae include passing the filter containing algae overa patterned, non-smooth surface roll, or applying a doctor or scraperblade directly to the upper filter surface. Since no substantialphysical forces have been applied to the algae because of the lowdifferential pressure at the upper surface relative to the lower surfaceof the filter, the algae is not driven significantly into the pores ofthe filter as long as the filter pores are sized properly relative tothe effective size of the algae particles, either singly or asagglomerated particles. The low moisture algae cake is thus relativelyeasy to remove, allowing the filter to be reused. Of course, if theeffective size of the algae particles (or a portion of the particles) issmaller than the pore size of the filter, those algae particles whichreach the pore are more likely to pass through, and optionally bere-collected below. The absorbent material may also be reused if aportion of the retained water can be repeatedly expelled, such as bypassing the material between two pinch rollers or other componentscapable of expressing liquid from the material such as a compressionroller, a vacuum, an air blower, a heater element, and a restrictiveplate pair. In one embodiment, the algae cake when dry (i.e., greaterthan 90% solids) would have a thickness of 25-900 microns (μ). Lesserthicknesses would be expected to result from the process of separatingsmaller diameter particles relative to those having large diameters.

In one embodiment, the absorbent material is in the form of a continuousloop or belt, with a direction of travel which is countercurrent to thatof a continuous loop filter belt. Configured in this way, with passageof the absorbent belt between components to express retained liquid, thedevice brings relatively low moisture absorbent material into contactwith the filter belt retaining the pool of algae mixture and thus havinga relatively high water content. This countercurrent travel arrangementthus tends to facilitate the transfer of water from the algae mixturethrough the filter pores. The structural integrity of the continuousfilter belt is improved by creating an edging along the edge borders ofthe belt. The belt is less prone to distortion by incorporating theedging. Rollers or clips can engage the filter edging to assist inproviding cross-web tension, and also to guide the filter belt. Thestructural integrity of the absorbent belt material is improved byaffixing a reinforcing material beneath the absorbent material. Goodresults were obtained by affixing a fiberglass window screen material asa webbing to the underside of the absorbent material, secured forexample by sewing the layers together. With continuous belts, it isimportant in use to have a seam presenting a low profile appearance sothat undue wear at the seam is minimized.

Also, it is contemplated that the pool containing an algae or otherparticulate mixture can receive a frothing device, such as an air bubblefrothing unit, or magnetic or electrical frothing devices (not shown),to concentrate particles such as algae at or near the surface of thepool. More particles at or near the surface of the pool result incomparatively fewer particles at or near the upper surface of thefilter, thus allowing comparatively more liquid to flow through thepores without being impeded or blocked by particles. To minimize energyconsumption, the efficiency improvement attributable to the flotationunit should be balanced against the increased energy consumptionattributed to operating that unit.

The absorbent material in one embodiment is described as a single,continuous loop or belt. Alternatively, the absorbent material may alsoinclude one or more absorbent rollers, or multiple continuous belts ofshorter length positioned beneath the filter, or combinations of shorterlength belts and rollers.

In an embodiment of the invention illustrated in FIGS. 1-7, the device10 has a separating section 12, a dewatering section 14, an optionaldrying section 15, and a collection section 16. In FIG. 3, a continuousloop filter belt 18 travels in a direction shown by arrow 20 driven by adrive roller 22 that is opposite a load roller 23. The filter belt 18may include a seam 27 having a low profile and/or a structure supportingthe filter material. Interior to the continuous loop formed by thefilter belt 18 is an absorbent belt 24 contacting the filter belt 18traveling in the opposite direction as shown by arrow 26. The absorbentbelt 24 may also form a continuous loop. The continuous absorbent beltis driven by a drive roller 28. A squeeze roller 30 is opposite thedrive roller 28, and applies pressure to squeeze out liquid from theabsorbent belt to be caught on a catch tray 31. Variable speed motorsdrive both the filter belt 18 and the absorbent belt 24 so that the beltspeeds and thus the device 10 can be adjusted as needed for a widevariety of input conditions. The motors may also be reversing, which maybe beneficial in certain situations, such as maintenance and repair, orto facilitate separation of different types of particles and liquids.The motors may include integral components for measuring energyconsumption, or be connected to discrete energy consumption devices tomeasure the power draw. The various components of the device are affixedto the frame 29.

A mixture input 32, for example a waterfall weir containing the mixtureof particles and liquid, is positioned to deposit the mixture, shown asan algal mixture 34 consisting of micro-algae 36 and water 38 in theseparating section 12. It has been found that, using the Euglena strainof algae, a solution of 3 grams of algae per liter of water provides amixture which has acceptable flow properties for conveying algae andseparating it from the water component. A solution of 100 g per liter ofwater for the Euglena strain has an unacceptably high viscosity whichinterferes with water removal through pores in the filter belt 18. Whenother strains are used, unacceptably high viscosities can be obtainedwith concentrations in a range of 60 to 100 g per liter of water. In oneembodiment, the concentration of solids (as particles) in liquid can bein the range of 2-3 g/liter. A concentration of 15 g/liter in anotherembodiment can be applied to a screen, with acceptable separation ofliquid. A solution of less than about 0.5 g algae per liter of watergenerally deposits too little algae on the surface of the filter belt 18to permit effective separation of an algae cake from the filter belt 18.The upper and lower concentration limits of the algal solution will varywith the algae strain being separated, the maturity (and thus theparticle size of the algae) and the presence (or lack thereof) of anyexudate or contaminants generated by the algae particles and depositedon the outer surface of individual particles.

It has also been found beneficial to deposit the mixture in an area ofthe filter belt 18 that has been configured to form a depression in theform of a well 40, to ensure that the mixture does not flow over theedges of the filter belt 18, and that a sufficient amount of mixture hasbeen added to provide a generally uniform coating of material across thewidth of the filter belt 18. The mixture may form a pool 42 in the well40, and the weight of the pool 42 and the edges of the filter belt 18 inthe separating area are supported by a bottom support 44 and side guides46. The bottom support 44 may be a curved piece of plastic, and the sideguides 46 may be stainless steel, but alternative designs and materialsof construction can be used. Further, one or both of the bottom support44 and the side guides 46 may not be required in an alternateconfiguration. The presence, absence, or dimension of the pool 42 iscontrollable by the rate of input of mixture 34, and the respectivespeeds at which the filter belt 18 and absorbent belt 24 are driven. Inone embodiment, the filter belt 18 receives edging 47 to assist instabilizing the belt, and to seal the fibers.

In operation, the mixture 34 is deposited on a top surface 48 of thefilter belt 18 in the well area 40. As shown in FIG. 1, the mixturesupply is introduced via a horizontally oriented pipe. However,alternate introduction components can be used, such as an overheadvertical pipe or an overhead manifold with multiple outlets spanningoptionally up to the entire width of the filter belt 18. The filter belt18 allows liquid such as water to pass through its pores 49 under theforce of gravity in a stream 50 (FIG. 3) which is collected in a catchpan 52. The pores are sized such that particles such as algae, of acertain size, either individually or as an agglomerate, are retained onthe top surface of the filter belt 18. As the particles such as algaeare mixed around in the pool 42 some of the particles settle on the topsurface 48 of the filter belt 18 at the bottom of the pool, while otherparticles continue to be agitated in the mixture. As the filter belt 18advances, a fresh surface area of filter enters the pool at the upstreamend 54 (FIG. 7) while a partly covered area of filter exits the pool atthe downstream end 56. As the filter exits the inclined sides of thepool, additional particles settle on the top surface 48. All theparticles on the filter form a wet cake 58 having water as shown in FIG.4. Though not shown, a froth flotation device, such as an aerator oracoustic, magnetic, or electrical concentrating devices, can be used toconcentrate particles at or near the surface of the pool 42, and thusaway from the top surface of the filter belt 18 to facilitate liquidflow through the pores of the filter belt 18.

As the filter belt 18 with wet cake advances, some water continues topass through the filter belt 18 pores by gravity. Additionally waterpassage through the filter pores and away from the algae is facilitatedby contacting the absorbent belt 24 to the lower surface 60 of thefilter belt 18. In one embodiment, the absorbent belt 24 nearest themixture supply end of the device 10 will contact the lower surface 60 ofthe filter belt 18 beneath a portion of the well area 40.

As the filter belt 18 advances the progressively lower moisture contentalgae cake, the bottom surface 60 of the filter belt 18 contacts andrests upon the top surface 62 of the absorbent belt 24. This absorbentbelt 24 in one embodiment travels in the opposite direction of thefilter belt 18, and alternatively travels at a different rate from thefilter belt 18, in either the co-current or counter-current direction.The absorbent material makes hydraulic contact with the water droplets64 forming and attempting to drop from the pores 49 of the filter belt18. FIG. 5 is drawn with a gap, to illustrate the water dropletsforming. Typically, however the two belts are actually in contact. Theabsorbent material wicks the liquid from filter pores, thus allowing thepores in the filter belt 18 to pull or receive liquid from theinterstitial spaces around the particles, with the liquid ultimatelybeing drawn into the absorbent material. Maintaining the moving filterbelt 18 in contact with the counter-rotating absorbent belt 24 allowsthe algae cake 58 to increase its solids content as it is exposed torelatively dry absorbent belt material.

As the section of the filter belt 18 having the particle cake breakscontact with the absorbent belt, at 66, it enters an optional dryingarea 15 that can further reduce moisture levels by any number of meansdepending on the needs of the process. The drying area may requirenothing else be done so that further drying takes place under ambienttemperature and humidity conditions. Or, one or more active dryingmethods may be used such as, for example, air movement, heating,dehumidification, sunlight, or combinations. These methods may beaccomplished with a heating element, a fan, a blower, a light source, anacoustic device, and/or a vacuum. In one embodiment the high solids cakepeels from the filter belt 18 once a moisture threshold is reached, andthe belt speeds and mixture input volumes can be varied so thatadditional drying becomes unnecessary. The porous structure of thefilter belt 18 also allows an active drying method such as air movementor heat to be applied to the particle cake from above the cake, belowthe cake, or both. Where the particle is algae, at approximately 34%solids and a thickness in the range of about 25 to 900 microns the algaecake will release from the upper surface of the filter belt 18, andbegin to form flakes.

At the collection section 16, the flexible filter belt 18 changesdirection at an angle of about 90 degrees or greater. The lower moisturealgae cake, being less flexible, cracks and falls off the belt to becollected. A variety of other collection enhancement methods may be usedas necessary. They include, for example, making a turn sharper than theradius turn illustrated around a roller. This can be done, for example,by passing the filter element over an edge to change direction oftravel, instead of the smooth radius roller. Scrapers, vibrators,blowers, augers, brushes, vacuums and the like may also be employed asneeded. However, it is desirable to maintain zero or near zero energyuse whenever possible. In addition, it is contemplated that filter beltsmay be used that have intentionally blocked off pores 68 such asillustrated in FIG. 6, which prevent forming a uniform cake. By workingwith an intentionally segmented cake rather than one large continuousone, the drying and peeling-up properties may be influenced, so thatcake is more easily separated from the filter belt. This is possiblebecause no forces, such as pressure differential (by vacuum drawingeffects, or air pressure pushing effects), or rollers or the like havebeen used that would contribute to drive the algae cells 36 into thepores 49 of the filter belt 18.

The device 10 includes one D.C. drive motor for causing movement of theflexible filter belt 18 relative to the frame 29 and a separate D.C.drive motor for causing movement of the absorbent material at a same ordifferent rate of speed. In one embodiment the energy utilized forharvesting and dewatering the algae to at least 20% solids, introducedas a dilute mixture in water can be less than 100 watts per kilogramalgae dewatered, in another embodiment less than 400 watts per kilogramalgae dewatered and in another embodiment less than 700 watts perkilogram algae dewatered when concentrating from a solution of 0.3 galgae/liter solution to at least 200 g/liter. In another embodiment, theenergy consumption is about 26 watts per kilogram algae dewatered whendewatering to at least 20% solids.

EXAMPLE

The following example illustrates the practice of one embodiment of theinvention using the device to dewater a particular strain of algae.Other embodiments within the scope of the claims herein will be apparentto one of skill in the art based on the disclosure herein.

The device was configured with a continuous filter made of Polyestermonofilament material (product number PES25/20) from SaatiTech, Somers,N.Y., having a pore size (also known as a mesh opening) of 25 micronsand an open area of 20%. Thickness of the filter was 52 microns, and theindividual thread diameter for preparing the filter material was 27microns. Beneath the filter belt was a continuous belt of airlaidnonwoven absorbent material, No. NF 52-230 made by Hagulan VliesstoffGmbH & Co. KG, Fulda, Germany. This belt was made of 80% viscose and 20%polyethylene. The structural integrity of the absorbent belt wasincreased by sewing a webbing of a fiberglass window screen material tothe underside. Both the continuous filter and continuous absorbent beltswere seamed to minimize thickness variations and thereby present smoothsurfaces relative to each other and the contacting components on theframe. The filter belt moved at a speed of 20.3 cm per minute (8inches/min.) driven by a DC Motor, to which was connected a Kill-a-wattwattmeter for measuring power draw.

An algae mixture made up of Chlorella vulgaris having an average(agglomerated) particle size of 10-40 microns (individual cell sizesranging from about 2 to about 10 microns), at a concentration of 0.8g/liter water, was poured into a pool defined by the moving filter belt,at a rate of 1.3 L/min. The absorbent material was moving countercurrentto the filter belt, at a speed of 15.2 cm per minute (6 inches/min.)driven by a DC Motor, to which was also connected a Kill-a-wattwattmeter.

Algae cake exiting the pool had an approximate solids content of about10%. Within about 15 cm travel of the cake on the filter belt withcountercurrent travel by the absorbent belt 24 beneath, the solidscontent increased to about 16%. Over the remaining 41 cm of the filterbelt 18 located above absorbent belt 24, the solids content increasedfurther, to about 18% solids by weight. At the end of the filter beltprior to the cake removal roller 43 the solids content was about 25%solids. Depending on the length of the filter belt and the ambientenvironmental conditions, further drying can occur without active dryingmeasures being taken. Elapsed time from initial introduction of thealgae mixture to removal of a cake having at least about 25% solids was8 minutes. Energy expenditure for the D.C. motors used to rotate therollers driving the filter 18 belt and absorbent belt 24 was 17 watts.The weight of algae cake of at least 20% solids produced in the steadystate mode per unit time was 3.7 g/min. Thus, 0.077 watt hours (277.2joules) of energy was expended to produce one gram of algae cake havinga 20% solids content. No other energy was expended to reach the solidscontent for the cake. The ambient temperature in the room wasapproximately 72° F. with a relative humidity of approximately 50%.

It can be appreciated that different strains of algae will havedifferent particle diameters at maturity. In addition, based on thestrain, and maturity of the algae, there may be a greater or lessertendency for individual algae particles to agglomerate, thus increasingthe effective size of the unit to be filtered. Also, the shape of theparticle may vary with the strain being used. Thus, the appropriatefilter screen material may have different pore sizes to effectivelyseparate the particles from water. Also, the flow rates of the mixturemay be varied to optimize particle recovery, and the water absorbingcapacity of the absorbent material may need to be appropriatelymodified. Thus, it is expected that ranges of algae strains, filterscreen pore sizes, and absorbance capacities can be utilized as desired.For further comparative information relative to the evaluation anddrying characterization for various algae strains, see Table 1 below.The separation conditions were generally the same as those set out abovein the Example.

TABLE 1 Botryococcus Chlorella Euglena Nannochloropsis Pond Water Algaebraunii vulgaris gracilis salina Marysville, OH Size Range 15-35 2-1015-40 0.5-2 0.5-40 (μm) Density (g/L) 2 2.8 3.1 40.2 1 Algae Energy 7.25.2 5.6 6.8 4.6 Content (Watt- hrs/gram Algae) # of Process 2 18 12 3953 Runs Flow Rate 456 342 342 60 510 (L/hr) Escaped 0.5 8 1 35 3 Algae(%)* Residual 1.2 0.5 1.4 0.4 1.0 Water in Dry Flake (%) Dry Solids 152147 175 261.3 83 Yield (g) *Escaped Algae are the percentage of Algaethat transferred with the water through the filter. Generally, thepercentage of algae particles which pass through the filter will notexceed 10-15% of the total particles quantity of algae particles.

An example of a filter screen that has been successfully used with theChlorella vulgaris microalgae is a woven polyester filter fabric (PES25/16) that may be obtained from SaatiTech of Somers, N.Y. The materialhas a mesh opening of 25 microns, a 16% Open Area, and a thread diameterof 34 microns. Air Permeability is 1,700 l/m²s (liters per square meterper second). The open area is defined as the percentage of pore surfaceto thread surface for a defined area of the filter fabric. The operativemesh opening is a function of the particle size of the material to beseparated from the liquid. A mesh opening substantially larger than theparticle size will result in most of the particles passing through thefilter belt. If the mesh opening is substantially smaller than theparticle size, the pores are more easily blocked or impeded, even withlow differential pressure. As a result, liquid movement is impeded,hampering the separation. It is generally acceptable to have up to about10% to 15% of the particles passing through the filter belt. Thus, thefilter belt mesh opening can be greater than the particle size, thoughnot substantially so. Thus, for example, a mesh opening of 25 micronswill effectively separate particles with an average size of about 20microns, with an acceptable amount of pass through particles. Ranges offilter material for use with the device can span from at least a 7micron mesh opening up to a 700 micron opening, with an open area of 2%up to 68%, respectively. In selecting the filter material, in oneembodiment the portion of the material closest to the mixture has thehighest hydrophobicity, with the material then becoming more hydrophilicas it extends away from the mixture. Coatings, such as those based onsilicone or fluorinated polymers, can be used to increasehydrophobicity.

Because of the low level of damage to individual algae particles in theseparation process, the filter belt 18 can run for extended timeswithout need to clean, replace or refurbish the material. In the formatset out in the Example, the filter belt 18 was operated for one weekbefore being taken off-line, soaked in a weak bleach solution for 20minutes, and returned to operation.

The absorbent material used for the absorbent belt was a needle feltfloor cloth (NF 52-230 S) having a weight of 221 g/m² (grams per squaremeter), a thickness of (for a 10 oz.) 2.2 mm, a blend of 80% Viscose and20% polyethylene and an absorption of 1198% or 2.65 liter/m² (liter persquare meter). It is available from Hagulan Vliesstoff GmbH & Co. KG, ofFulda Germany.

Although the above invention has been described in terms of use for thedrying of algae, it is also useable for the separation, dewatering, andcollection of any other particulate matter from water or another liquid.The properties of such other particulate matter may require adjustingthe characteristics of the screen and absorbent layer, so that thescreen and absorbent layer are non-reactive with the liquid or theparticles. Also, other liquids than water could be used. For example,particulate matter from an ethanol production process were separatedfrom the liquid carrier, as was particulate matter from waste water usedin an oil recycling operation.

The embodiment illustrated and described herein has a single absorbentbelt traveling within the screen for the purpose of separating the algaefrom water or other liquid in which it is grown or conveyed. It is alsoenvisioned that other processes can be carried out on the algae while itis on the screen belt, or after it is transferred to another belt. Forexample, the traveling screen belt may pass under a nozzle that sprayssolvent on the algae cake for the purpose of removing oils or othersubstances present on the exterior of the algae. This solvent would thenpass through the screen and be collected. The desirable material, forexample a lipid, could then be separated from the solvent and thesolvent re-circulated. Also, a second absorbent belt may be brought intocontact with the bottom of the filter belt, to assist in furtherreducing the moisture level of the algae cake before its finalcollection. It is contemplated that during the process of removingorganic material from the outside surface of the algae particles, thealgae may be kept alive and undamaged, so that they can be returned tothe tank to produce more material on the outside surface. Since algaethat produce materials extracellularly often have a slower rate ofreproduction, this frequent harvesting of organic material from theoutside surface and return would be used to keep production rates at adesired level.

The embodiment illustrated and described herein employed a horizontallyoriented belt surface. Variations in orientation are possible. It isalso envisioned that a device may be configured having a round disk offilter screen traveling in a first direction around an axis and a diskof absorbent material traveling the opposite direction around a secondaxis, along with an appropriate way of removing the cake material, forexample with a scraper or a vacuum. Similarly, the device may be made inthe form of cylinders, for example with the algae being placed on theoutside of a cylinder of screen, and an absorbent material on theinside.

While the invention has been illustrated by a description of variousembodiments and while these embodiments have been described inconsiderable detail, it is not the intention of the Applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Thus, the invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative example shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of Applicants' general inventive concept.

1. A device for separating particles from a liquid comprising: a frame,a filter, an absorbent layer, and at least one movement device soconstructed and located relative to said frame to cause relative countercurrent movement between the filter and the absorbent layer; the frameconstructed and arranged to support the filter and the absorbent layerand to allow the filter and absorbent layer to move counter currentrelative to one another; the filter including an upper surface, a lowersurface, and pores extending between the upper and lower surfaces; theabsorbent layer including an upper surface and a lower surface; and atleast a portion of the lower surface of the filter contacting at least aportion of the upper surface of the absorbent layer while moving inrelative counter current directions, wherein the contact between thelower surface of the filter and the upper surface of the absorbent layeris sufficient to effect the separation of at least a portion of theparticles from at least a portion of the liquid by movement of theportion of liquid through the pores of the filter and into the absorbentlayer without application of an external force to the mixture whileretaining at least a portion of the particles on the upper surface ofthe filter.
 2. The device of claim 1 wherein the upper surface of thefilter is hydrophobic relative to the lower surface.
 3. The device ofclaim 1 wherein the filter is a continuous loop.
 4. The device of claim3 wherein the continuous loop filter includes edging.
 5. The device ofclaim 1 wherein the absorbent layer is a continuous loop.
 6. The deviceof claim 1 further comprising a device for removing particles from theupper surface of the filter after separation of at least a portion ofthe liquid.
 7. The device of claim 6 wherein the particle removingdevice is at least one of a scraper, a vacuum, a brush, a vibrator, andan auger.
 8. The device of claim 6 further comprising a collector forcollecting particles removed from the filter.
 9. The device of claim 6further comprising at least a second device for removing liquid from amixture containing liquid and particles in addition to the absorbentlayer.
 10. The device of claim 9 wherein the at least second device isat least one of a heating element, a fan, a blower, a light source, anacoustic device, and a vacuum.
 11. The device of claim 1 furthercomprising a device configured to remove liquid from the absorbentlayer.
 12. The device of claim 11 wherein the liquid removing device isat least one of a compression roller, a pair of pinch rollers, a vacuum,an air blower, a heater element, and a restrictive plate pair.
 13. Thedevice of claim 1 wherein at least a portion of the upper surface of thefilter forms a depression in which a mixture containing liquid andparticles may pool.
 14. The device of claim 1 further comprising adevice to concentrate particles at an upper surface of a mixturecontaining liquid and particles.
 15. The device of claim 14 wherein theconcentrating device is at least one of an aerator, an electronicdevice, a magnetic device, and an acoustic device for concentratingparticles at the surface of the mixture.
 16. The device of claim 1further comprising a mixture input for providing a mixture containingliquid and particles to the upper surface of the filter wherein themixture input is at least one of a waterfall weir, at least one nozzle,a manifold, and a plurality of nozzles.